Forms :: Find And Update A Record Using Multiple Criteria

I Have a forms which brings up a record in textboxes when you hit a search Button using a value that you type into a Textbox called BarTxt. My problem is that this value may not be unique. Therefore I'm trying to find and update the table using 2 values from the table (Barcode and PurchaseOrder).I have entered the code

Code:

Private Sub SearchBtn_Click()
PNTxt = DLookup("PartNumber", "BookInTable", "BarCode ='" & [BarTxt] & "'" And "PurchaseOrder ='" & [POTxt] & "'")
End Sub

This however is just bringing up a Type mismatch error. Even though both are text fields.Also even if I just use Barcode to search which works. My update Code

Code:

DoCmd.RunSQL "Update BookInTable SET DateBookedOut = '" & Me!DateTxt & "' WHERE BarCode ='" & [BarTxt] & "'" AND PurchaseOrder ='" & [POTxt] &

I get an Compile error saying "expected expression".